This is my last post in this thread as the OP just isnt even capable of doing anything with my posts...
Why are you insisting that you must record to a mac? What kind of reasoning is that? Digital video is just that, a digital file of a video.
How do you get that file onto your computer so you may edit it (in Final Cut, After Effects, iMovie etc etc, I suggested this already but you seem to have missed that) is the problem I think you are struggling with...
You do not need to hit record on your computer and point a camera at something to get a digital video file on your machine.
If you want to have a webcam hooked up to your computer and record, fine. But you would need a SECOND computer to record the second webcam. AFAIK you cant use 2 webcams at the same time...if this is what you want, google more....EDIT: seems the above link to the apple discussion can answer that.
2 angles = 2 recordings = 2 video files = 2 ways to record
the best way to get 2 videos is with 2 video camcorders. These will record your 2 angles onto 2 tapes. Then when you are done recording, you would use your video app of choice (see above for numerous examples) to capture the footage from the tape to your computer.
then you would edit your 2 files, sync them up and do whatever it is you want to make them split screen.
if you are asking "is there an application to do all this for me?" the answer is a resounding no. You do not need to record this LIVE for any reason. Its only going to complicate things.